Infer categorized watcher group names from actual host execution

- update the watcher to stop trusting misleading categorized child build labels when they do not match the host/spec actually being executed
- infer the reported categorized group name from the actual host being run, so mismatched labels like ubuntu-batch for a Red Hat host are corrected in status reporting
- document the categorized watcher workaround in the ATVM guide, watcher design, and watcher README without changing the underlying ATVM runner scripts

atvm/docs/automation/guide.md

@@ -47,6 +47,7 @@ Run ATVM CMC automation tests on the designated automation VM without unintended
   - it must post one final Mattermost status per completed categorized group/sub-run
   - it must stay active between grouped sub-runs while the parent categorized request is still running
   - it must not stop after the first grouped run simply because one grouped run completed
+  - if the child build id label does not match the actual host/spec being executed, report the grouped run using the inferred host-based group instead of the raw child build id label
   - it must not wait and replace those with one single parent-only post
 - After execution, report immediate success/failure only.
 - Do not actively monitor completion unless explicitly requested.

atvm/docs/automation/mattermost-watcher-design.md

@@ -44,6 +44,7 @@ A categorized run must be treated differently:
 - then continue watching for the next grouped sub-run
 - the watcher must remain alive while the parent categorized request or related child Cypress process is still active
 - one completed grouped sub-run must not be treated as proof that the parent categorized request is finished
+- if the child build id label does not match the actual host/spec being executed, the watcher must infer the real group from host execution and use that inferred group for reporting
 - the watcher must not wait until the very end to send one single parent-only post
 
 Evidence sources: